The present invention generally relates to a thin film magnetic head and in particular concerns a thin film magnetic head of magnetic induction type which is adapted for use in magnetic drums, magnetic tapes or magnetic discs for electronic computer systems.
The thin film magnetic head of the magnetic induction type (hereinafter simply referred to as the thin film magnetic head) is realized with the aid of the thin film technology and so designed as to attain a high recording density in the magnetic recording on a magnetic drum, a magnetic tape or a magnetic disc. To this end, the thin film magnetic head includes in a laminated structure a lower or underlying magnetic film and an upper or overlying magnetic film which cooperate together to constitute a magnetic circuit having a magnetic gap at a predetermined location, a conductor film extending between the lower and the upper magnetic films and forming a coil having a predetermined number of turns which intersect the magnetic circuit, and an insulating layer or member for electrically mutually insulating the individual turns of the conductor coil or film and insulating the conductor film, the lower magnetic film and the upper magnetic film from one another. The laminated structure is of course realized on a substrate through a series of thin film processings, which substrate may be partially or wholly made of a magnetic material so that it may also serve as the lower or underlying magnetic member.
The read-out or output characteristic as well as the electromagnetic transducing characteristic of the thin film magnetic head mentioned above has a large dependency on the magnetic characteristics of the magnetic film. Since the thin film magnetic head is used in a high frequency region, it is required that the magnetic film should exhibit high permeability under the high frequency region in concern. To meet with this requirement, the magnetic film has to be imparted with such uniaxial magnetic anisotropy that the axis of easy magnetization of the magnetic film extends in the direction widthwise of the record track traced by the thin film magnetic head, wherein magnetic excitation is effected in the direction corresponding to the axis of hard magnetization in view of the fact that magnetization reversal is then realized by rotation of magnetization at a significantly higher speed as compared with the magnetization reversal realized by domain wall motion which is brought about when the magnetic excitation is effected in the direction corresponding to the easy axis.
On the other hand, one of the requirements imposed on the thin film magnetic head is to reduce or nullify the instability of the electromagnetic transducing characteristic which is considered to be ascribable to the fact that difference in dimension of the magnetic films is insignificant when compared with the size of the magnetic domain and that the magnetic head is used in the high frequency region on the order of MHz or more and which presents no problem in the conventional bulk magnetic head. In efforts to solve this problem, there have heretofore been proposed various measures.
It is proposed as one of the approaches for solving the aforementioned problem to use the magnetic film which exhibits a negative magnetostriction constant on the grounds that the axis of hard magnetization can then extend perpendicularly to the direction widthwise of the recording track traced by the magnetic head because of the tensile stress acting on the magnetic film in the direction perpendicular to the direction widthwise of the track and that the magnetic switchings of the major magnetic domains take place progressively under smooth rotation of magnetization. However, experiments performed by the inventors have shown that there are produced in the upper magnetic film such tensile stresses which act in the direction widthwise of the recording track and compressive stresses which act in the direction perpendicular to the direction widthwise of the recording track in addition to the tensile stresses acting in the direction perpendicular to the direction widthwise of the track, and that the negative magnetostriction constant of a large value is undesirably accompanied with decrease in the permeability of the magnetic film. It has thus been established that the thin film magnetic head enjoying the stable electromagnetic transducing characteristic can not be attained merely by imparting the negative magnetostriction to the magnetic film.
As another approach, it is also known to make the composition of the magnetic film uniform. Since the magnetostriction of the magnetic film is mainly determined by the composition thereof, the uniform composition will bring about the correspondingly uniformed magnetostriction which in turn will be able to make the electromagnetic transduction characteristic more stable when compared with the magnetic head in which the magnetostriction of the upper magnetic film is not uniform. However, since the electromagnetic transducing characteristic undergoes influences of other various factors mentioned hereinbefore in addition to the magnetostriction, it is impossible to assure sufficient stability for the electromagnetic transducing characteristic by merely making the composition uniform and hence the magnetostricticn of the magnetic film.